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vhost: lockless enqueuing

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We use spinlock to synchronize the work list now which may cause
unnecessary contentions. So this patch switch to use llist to remove
this contention. Pktgen tests shows about 5% improvement:

Before:
~1300000 pps
After:
~1370000 pps

Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Jason Wang 2016-04-25 22:14:33 -04:00 committed by Michael S. Tsirkin
parent 7235acdb11
commit 04b96e5528
2 changed files with 29 additions and 30 deletions
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52
drivers/vhost/vhost.c
View File

@ -168,7 +168,7 @@ static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
{
INIT_LIST_HEAD(&work->node);
clear_bit(VHOST_WORK_QUEUED, &work->flags);
work->fn = fn;
init_waitqueue_head(&work->done);
}
@ -246,15 +246,16 @@ EXPORT_SYMBOL_GPL(vhost_poll_flush);
void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
{
unsigned long flags;
if (!dev->worker)
return;
spin_lock_irqsave(&dev->work_lock, flags);
if (list_empty(&work->node)) {
list_add_tail(&work->node, &dev->work_list);
spin_unlock_irqrestore(&dev->work_lock, flags);
if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
/* We can only add the work to the list after we're
* sure it was not in the list.
*/
smp_mb();
llist_add(&work->node, &dev->work_list);
wake_up_process(dev->worker);
} else {
spin_unlock_irqrestore(&dev->work_lock, flags);
}
}
EXPORT_SYMBOL_GPL(vhost_work_queue);
@ -262,7 +263,7 @@ EXPORT_SYMBOL_GPL(vhost_work_queue);
/* A lockless hint for busy polling code to exit the loop */
bool vhost_has_work(struct vhost_dev *dev)
{
return !list_empty(&dev->work_list);
return !llist_empty(&dev->work_list);
}
EXPORT_SYMBOL_GPL(vhost_has_work);
@ -305,7 +306,8 @@ static void vhost_vq_reset(struct vhost_dev *dev,
static int vhost_worker(void *data)
{
struct vhost_dev *dev = data;
struct vhost_work *work = NULL;
struct vhost_work *work, *work_next;
struct llist_node *node;
mm_segment_t oldfs = get_fs();
set_fs(USER_DS);
@ -315,29 +317,25 @@ static int vhost_worker(void *data)
/* mb paired w/ kthread_stop */
set_current_state(TASK_INTERRUPTIBLE);
spin_lock_irq(&dev->work_lock);
if (kthread_should_stop()) {
spin_unlock_irq(&dev->work_lock);
__set_current_state(TASK_RUNNING);
break;
}
if (!list_empty(&dev->work_list)) {
work = list_first_entry(&dev->work_list,
struct vhost_work, node);
list_del_init(&work->node);
} else
work = NULL;
spin_unlock_irq(&dev->work_lock);
if (work) {
node = llist_del_all(&dev->work_list);
if (!node)
schedule();
node = llist_reverse_order(node);
/* make sure flag is seen after deletion */
smp_wmb();
llist_for_each_entry_safe(work, work_next, node, node) {
clear_bit(VHOST_WORK_QUEUED, &work->flags);
__set_current_state(TASK_RUNNING);
work->fn(work);
if (need_resched())
schedule();
} else
schedule();
}
}
unuse_mm(dev->mm);
set_fs(oldfs);
@ -398,9 +396,9 @@ void vhost_dev_init(struct vhost_dev *dev,
dev->log_file = NULL;
dev->memory = NULL;
dev->mm = NULL;
spin_lock_init(&dev->work_lock);
INIT_LIST_HEAD(&dev->work_list);
dev->worker = NULL;
init_llist_head(&dev->work_list);
for (i = 0; i < dev->nvqs; ++i) {
vq = dev->vqs[i];
@ -566,7 +564,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
/* No one will access memory at this point */
kvfree(dev->memory);
dev->memory = NULL;
WARN_ON(!list_empty(&dev->work_list));
WARN_ON(!llist_empty(&dev->work_list));
if (dev->worker) {
kthread_stop(dev->worker);
dev->worker = NULL;

7
drivers/vhost/vhost.h
View File

@ -15,13 +15,15 @@
struct vhost_work;
typedef void (*vhost_work_fn_t)(struct vhost_work *work);
#define VHOST_WORK_QUEUED 1
struct vhost_work {
struct list_head node;
struct llist_node node;
vhost_work_fn_t fn;
wait_queue_head_t done;
int flushing;
unsigned queue_seq;
unsigned done_seq;
unsigned long flags;
};
/* Poll a file (eventfd or socket) */
@ -126,8 +128,7 @@ struct vhost_dev {
int nvqs;
struct file *log_file;
struct eventfd_ctx *log_ctx;
spinlock_t work_lock;
struct list_head work_list;
struct llist_head work_list;
struct task_struct *worker;
};